Page 117 - Handbook of Adhesives and Sealants

Theories of Adhesion 85

Figure 2.19 Effect of crosslink density on the physical state of epoxy resins. 21

Adhesive formulators use the glass transition temperature, T ,asa
g
practical basis for compounding products with the appropriate amount
of internal motion. T is the temperature at which the slope of a tem-
g
perature-volume plot undergoes a sudden upward change shown in
Fig. 2.20. It is the temperature at which there is significantly more
molecular mobility than at lower temperatures (i.e., the molecules
have sufficient thermal energy to be considered mobile). T is a prop-
g

Volume

T g

Temperature
Figure 2.20 The effect of temperature on the total volume
of a polymer.